The present invention relates to a capacitor applicable to a semiconductor integrated circuit and a manufacturing method of the capacitor. Especially, the capacitor according to the present invention is a capacitor having large capacity and high voltage resistance, thus being suitable for an analog circuit.
One of known capacitors used for a semiconductor device is a capacitor for DRAM (Dynamic Random Access Memory).
Recent design rule to be applied to the DRAM is given in sub micrometers, and required operation voltage has been reduced down to approximately 1.1V. That is, DRAM has required larger scaled integration and lower operation voltage. To overcome those technical difficulties, various structures and manufacturing methods have been proposed.
For example, Unexamined Japanese Patent Application KOKAI Publication No. H9-121035 discloses a method for manufacturing a capacitor. According to the disclosed technique, a capacitor is manufactured by the following steps. A lower electrode (storage electrode) is formed first, and tantalum oxide is deposited onto the lower electrode. Then, the wafer is annealed under an oxygen atmosphere, thus, oxygen vacancy in the tantalum oxide is removed while the tantalum oxygen is recrystallized. After performing the deposition and crystallization of the tantalum oxide several times, an upper electrode (common electrode) is formed, thus the fabrication of the capacitor is completed.
Unexamined Japanese Patent Application KOKAI Publication No. H10-74898 also discloses a method for manufacturing a capacitor. According to the method, a capacitor is manufactured by the following steps. A lower electrode made of polysilicon is formed first. The surface of the lower electrode is subjected to rapid thermal nitridation and rapid thermal oxidation, and then tantalum oxide is deposited onto the surface. The wafer is annealed under an oxygen atmosphere to remove oxygen shortage while recrystallizing the tantalum oxide. An anti-diffusion film made of titanium nitride or the like is formed on the surface. Finally, an upper electrode is formed thus the fabrication of the capacitor is completed.
Another method disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H11-135756 teaches the following steps for manufacturing a capacitor. A lower electrode made of doped polysilicon is formed first. Then, the lower electrode is nitrided, and tantalum oxide is deposited onto the nitrided lower electrode. The wafer is annealed under an oxide atmosphere, and wet oxidization and dry oxidization are carried out to crystallize the tantalum oxide. An anti-diffusion film made of titanium nitride or the like is formed on the surface. Finally, an upper electrode is formed, thus, the fabrication of the capacitor is completed. According to this method, the nitride film acts as a barrier film for oxidization during the wet and dry oxidation steps, thus, the lower electrode is prevented from being oxidized.
Other than DRAM, the capacitors are useful for analog circuits such as an audio circuit, an RF (Radio Frequency) circuit and a power supply circuit. In the field of the analog circuits, capacitors having large capacitance are necessary for driving the circuits with an operation voltage in a range of 3.3 to 15 V or higher. The above described techniques for fabricating capacitors are not suitable for manufacturing the capacitors having large capacitance and excellent high voltage resistance. For example, maximum allowable voltage for a tantalum oxide film whose thickness is suitable for DRAM is only approximately 1.2 V. This is caused by a tunnel current which influences greatly as higher voltage is applied. Thicker tantalum oxide film merely raises the allowable voltage up to approximately 3 V. This is caused by oxygen vacancies remaining in the tantalum oxide film even if the tantalum oxide film has been oxidized and crystallized. Further, the thicker the tantalum oxide film becomes, the easier the vacancies appears. Therefore, it is difficult to form a thick tantalum oxide film without oxygen vacancies in the case of an analog circuit which requires a thick tantalum film.
In consideration of the above, a capacitor having large capacitance and excellent high voltage resistance with using a dielectric film and a method of manufacturing such a capacitor have been required.
The present invention was made in consideration of the above, it is an object of the present invention to provide a capacitor having large capacitance and excellent high voltage resistance, and a method for manufacturing the capacitor.
It is another object of the present invention to provide a proper capacitor suitable for an analog circuit, and a method for manufacturing the capacitor.
It is still another object of the present invention to provide a large capacitance capacitor which uses a dielectric film to withstand 3.3 V or more for an analog circuit, and a method for manufacturing the capacitor.
A method for manufacturing a capacitor for an analog circuit comprises the steps of:
forming a semiconductor layer (15) to be a first electrode;
forming a dielectric film (23) on the semiconductor layer (15);
oxidizing the semiconductor layer (15) via the dielectric film (23) to form an oxide film between the semiconductor layer (15) and the dielectric film (23); and
forming a second electrode (25) on the dielectric film (23) so as to face the first electrode (15).